3,606 research outputs found

    Observation of the decay Zψ+μ+μ+\mathrm{Z}\to\psi\,\ell^+\ell^-\to\mu^+\mu^-\ell^+\ell^- with the CMS detector

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    The observation of the Z\mathrm{Z} boson rare decay to a ψ\psi meson and two oppositely charged same-flavour leptons, +\ell^+ \ell^-, where ψ\psi represents the sum of J/ψ\mathrm{J}/\psi and ψ(2S)J/ψX\psi(\mathrm{2S})\to\mathrm{J}/\psi\, X, and =μ,e\ell=\mu,\mathrm{e}, is presented. The data sample used corresponds to an integrated luminosity of 35.9fb135.9\,\mathrm{fb}^{-1} of proton-proton collisions at a center-of-mass energy of 13TeV13\,\mathrm{TeV} accumulated by the CMS experiment at the LHC. The signal is observed with a significance in excess of 5 standard deviations. Removing contributions from ψ(2S)\psi(\mathrm{2S}) decays to J/ψ\mathrm{J}/\psi, the signal is interpreted as being entirely from ZJ/ψ+\mathrm{Z}\to\mathrm{J}/\psi\,\ell^+\ell^-, with its fiducial branching fraction relative to that of the decay Zμ+μμ+μ\mathrm{Z}\to\mu^+\mu^-\mu^+\mu^- measured to be B(ZJ/ψ+)B(Zμ+μμ+μ)=0.70±0.18(stat)±0.05(syst).\frac{\mathcal{B}(\mathrm{Z}\to\mathrm{J}/\psi\,\ell^+\ell^-)}{\mathcal{B}(\mathrm{Z}\to\mu^+\mu^-\mu^+\mu^-)}=0.70\pm 0.18\, \mathrm{(stat)} \pm 0.05\, \mathrm{(syst)}. This result is obtained with the assumption of no J/ψ\mathrm{J}/\psi polarisation, where extreme polarisation scenarios can create 24%-24\% to +22%+22\% variations

    Identification of circles from datapoints using Gaussian sums

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    We present a pattern recognition method which use datapoints on a plane and estimates the parameters of a circle. MC data are generated in order to test the method's efficiency over noise hits, uncertainty in the hits positions and number of datapoints. The scenario were the hits from a quadrant of the circle are missing is also considered. The method proposed is proven to be robust, accurate and very efficient.Comment: 4 pages, 5 figure

    Performance Studies of a Micromegas Chamber in the ATLAS Environment

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    Five small prototype micromegas detectors were positioned in the ATLAS detector during Large Hadron Collider running at s=7\sqrt{s} = 7 and 8TeV8\, \mathrm{TeV}. A 9×4.5cm29\times 4.5\, \mathrm{cm^2} double drift gap detector was placed in front of the electromagnetic calorimeter and four 9×10cm29\times 10\, \mathrm{cm^2} detectors on the ATLAS Small Wheel, the first station of the forward muon spectrometer. The one attached to the calorimeter was exposed to interaction rates of about 70kHz/cm270\,\mathrm{kHz}/\mathrm{cm^2} at L=5×1033cm2s1\mathcal{L}=5\times 10^{33}\,\mathrm{cm^{-2}s^{-1}} two orders of magnitude higher than the rates in the Small Wheel. We present the results from performance studies carried out using data collected with these detectors and we also compare the currents drawn by the detector installed in front of the electromagnetic calorimeter with the luminosity measurement in ATLAS.Comment: 9 pages, 11 figure